England [ Images ] won the first one-day international against South Africa [ Images ] by 26 runs at Johannesburg on Sunday on the Duckworth/Lewis method after rain washed out play 25.1 overs into the England innings.
South Africa had struggled to 175 for nine in their 50 overs and England had reached 103 for three when the Wanderers outfield was swamped by heavy showers.
The teams walked off the field at 4.05 p.m. local time and play was called off about 90 minutes later.
England had won the toss and sent South Africa in to bat. Wickets fell regularly as South Africa slumped to 90 for seven before the experienced duo of Shaun Pollock [ Images ] (37) and Nicky Boje (33) boosted the innings with an eighth-wicket stand of 58.
Slow left-armer Ashley Giles picked up three lower-order wickets. Pacemen Darren Gough, Matthew Hoggard [ Images ] and Kabir Ali took two wickets each to get rid of the top-order.
South African captain Graeme Smith [ Images ] said: "We played some poor shots under pressure and although we did well to get to 175 in the end, another 20 or 30 runs would have made the game very competitive."
England skipper Vaughan praised Pietersen, who is looking to fill the gap caused by Andrew Flintoff's [ Images ] return home for ankle surgery.
Vaughan said: "He plays shots that make you stand at the other end in awe. They came at him hard as you would expect them to do and he was pretty nervous for the first four or five balls.
"But his composure impressed me and he seems to be the kind of guy who has the confidence to handle those sorts of situations."
South African-born Pietersen secured his place in Sunday's line-up after scoring 97 in a warm-up match against South Africa A where he brushed off taunts from the opposition.
The second one-dayer in the seven-match series is in Bloemfontein on Wednesday. England won the Test series 2-1.
G.Smith c Strauss b Gough 1
H.Gibbs c Pietersen b Hoggard 2
J.Kallis c G.Jones b Ali 5
A.Bacher b Hoggard 4
A.Prince lbw b Ali 22
J.Kemp c Bell b Giles 24
M.Boucher b Giles 17
S.Pollock c Vaughan b Giles 37
N.Boje b Gough 33
M.Ntini not out 10
A.Nel not out 1
Extras (b-3 lb-11 nb-1 w-4) 19
Total (for nine wickets, 50 overs) 175
Fall of wickets: 1-3 2-5 3-19 4-41 5-49 6-83 7-90 8-148 9-170
Bowling: Gough 10-2-27-2 (w-2), Hoggard 10-2-35-2, Ali 8-1-29-2, Collingwood 7-0-21-0 (w-2), Trescothick 8-0-31-0 (nb-1), Giles 7-0-18-3
M.Trescothick c Kallis b Ntini 11
G.Jones c Boucher b Pollock 8
M.Vaughan not out 44
A.Strauss c Kemp b Nel 15
K.Pietersen not out 22
Extras (lb-2 w-1) 3
Total (for three wickets, 25.1 overs) 103
Did not bat: P.Collingwood, I.Bell, A.Giles, K.Ali, D.Gough, M.Hoggard.
Fall of wickets: 1-19 2-21 3-44.
Bowling: Pollock 8-3-19-1, Ntini 7-0-29-1, Nel 5-2-13-1 (w-1), Kemp 3-0-25-0, Boje 1-0-8-0, Kallis 1.1-0-7-0.
Result: England won by 26 runs, D/L method.